Project 5: Multimorbidity?Abstract There is considerable interest in understanding patterns, determinants and consequences of multimorbidity in aging populations, but relatively little research has been conducted outside of high-income settings. The population of sub-Saharan Africa is aging rapidly, resulting in a rising burden of multiple chronic conditions, with additional complexity derived from the high prevalence of HIV infection, especially in the era of increasing survivorship through antiretroviral therapy. As the population ages, conditions affecting cognitive function, notably Alzheimer's disease and related dementias, contribute further to a complex profile of multimorbidity. Multimorbidity likely has significant implications for physical and cognitive functioning, mental health, mortality risks, health service utilization and costs. The concept of frailty has been advanced as a way to characterize a consistent aging phenotype that combines indicators of health and functional status that are highly predictive of health decline and mortality, and the connection between multimorbidity and frailty is important to understand in organizing health systems and planning for both formal and informal care of aging populations. This project uses multimorbidity as an integrative lens through which to unify many of the major empirical observations in the study cohort, and to amplify important themes relating to social and economic drivers of health outcomes in aging populations that link all of the projects in the program. Our overall goal is to illuminate the role of multimorbidity at the nexus of a complex web of determinants, outcomes and consequences. Toward this end the project has four specific aims: AIM 1: Develop a comprehensive portrait of the epidemiology of multimorbidity in a cohort of older South Africans, including its prevalence and degree, its incidence and trajectory, and its patterns and determinants. AIM 2: Evaluate the consequences of multimorbidity on mortality, physical and mental function, and well- being. AIM 3: Assess the implications of multimorbidity for healthcare service utilization, effective coverage, and health care spending. AIM 4: Quantify the relationship between multimorbidity and frailty, and associated excess mortality risks, and develop integrative measures of healthy life expectancy.